1. Field of the Invention
The present invention relates to electronic equipment such as an electronic typewriter having a character sequence memory and a character display.
2. Description of the Prior Art
In a modern electronic typewriter, the keyboard and the print unit of a mechanical typewriter have been implemented electronically so that various disadvantages encountered in the mechanical typewriter are eliminated, a relatively good key depression touch is obtainable and various functions are attained.
Such an electronic typewriter uses a memory for executing various functions. A high integration density of memory cells is attainable in such a memory and a low cost and relatively large capacity non-volatile memory is available without relying on an external storage such as a magnetic storage. Such a memory is used to store a sequence of characters. In the typewriter having a character sequence memory, an index comprising one or more characters is allotted to each of frequently used idiomatic phrases, words and addresses in order to register a plurality of such idioms in the memory of the typewriter. On the other hand, the character sequence registered in the memory can be read out and printed out.
In the prior art electronic typewriter, however, in order to allow correction such as insertion or deletion of a character sequence, it is necessary to limit a length of the character sequence to be corrected or to provide a large capacity memory for the correction. In addition, it is difficult for an operator to use the entire character sequence memory.
For example, FIG. 1 shows a schematic block diagram of a partial configuration of a prior art electronic equipment having a character sequence memory. A character sequence memory 1 and a character sequence correction buffer 2 are connected to a signal line CS for defining read/write timing and an address data bus ADB, respectively. Data are written into or read from a memory location specified by an address appearing on the address data bus ADB in accordance with the read/write timing signal appearing on the signal line CS. As shown in FIG. 2, the character sequence memory 1 contains four directories (indexes), DIR(A), DIR(B), DIR(C) and DIR(D) and corresponding character sequences (A), (B), (C) and (D). Each of the directories, for example, the directory DIR(B), comprises an 8-byte index (ID), a 2-byte start address (address information field ADR) for the corresponding character sequence and a 2-byte effective character count information field (CNT) as shown in FIG. 3. The character sequences (A), (B), (C) and (D) are coded characters (e.g. by an ASCII code) and the lengths of the character sequences are variable. In such a configuration, when it is desired to correct the character sequence (B) (for example, to insert or delete a character or characters), the content of the character sequence (B) is written into the character sequence correction buffer 2 through the address data bus ADB and the desired character or characters are inserted or deleted. After the sequence of a correction operation is completed, the corrected character sequence is transferred immediately behind the character sequence (D) in the character sequence memory 1 and stored therein. As a result, the character sequence (B) in FIG. 2 becomes an invalid character sequence and the directory DIR(B) has the address information and the character count information updated, as shown in FIG. 4.
When such a prior art character sequence memory control method is applied to the electronic typewriter, only a limited area is utilized and the character sequence memory 1 cannot be utilized efficiently. In addition, as described above, since the invalid character sequence appears, an operation to delete the invalid character sequence is required and a large capacity character sequence correction buffer 2 is required. The number of characters to be inserted for a given character sequence is undefined and the capacity of the character sequence correction buffer 2 must be as large as possible so long as the capacity of the character sequence memory 1 permits the insertion.
In the character sequence memory 1 used in the prior art electronic typewriter, the number of indexes which can be registered is limited and it is difficult to register a number of short character sequences, or when a plurality of short character sequences are registered memory areas which are not used nevertheless appear in the character sequence memory 1 and hence a very low efficiency character sequence memory 1 results.
For example, when it is desired to add short character sequences (E), (F) and (G) in the configuration of FIG. 1, the memory 1 has two vacant fields 1A and 1B as shown in FIG. 2 and hence the directories DIR(E) and DIR(F) and the corresponding character sequences (E) and (F) can be added, but a directory DIR(G) for the character sequence (G) cannot be formed in spite of the fact that the character sequence memory 1 includes unused memory areas as shown in FIG. 8. Thus, a character sequence (G) cannot be stored in the character sequence memory 1. This is caused by the fact that the character sequence memory 1 is split into the directory fields DIR(A)-DIR(F) and the character fields (A)-(F) in order to simplify the character sequence insertion operation. Thus, the prior art character sequence memory 1 has been used in a very inefficient manner.
The electronic typewriter having a character sequence memory 1 as described above can register specific sentences or frequently used idiomatic phrases, words or addresses in the memory 1, and a selected one of the registered character sequences can be accessed by a keying operation, corrected as required and printed out. In such an electronic typewriter, a character display is used to permit reference to characters input thereto.
However, in most of the prior art character displays, on the order of 20 characters may be shown. Thus, when a registered character sequence having heading blank characters which extend beyond the number of characters permitted to be shown by the character display is to be referred to by the keying operation, a blank is displayed by the first keying operation. This presents a feeling of unrest to the operator. Since the reference of the character sequence is carried out by using the character display and the keyboard, the electronic typewriter displays the heading characters of the accessed character sequence, but if all of the 20 characters accessed by the first keying operation are blank characters, the operator may regard it as a failure of the character operation. If the next 20 characters which are displayed by the second keying operation are also blank characters, the same occurrence results. In addition, the keying operation for accessing the all-blank character sequence is wasteful.
In the 20-character character display, it is not possible to display the entire character sequence in one operation. Thus, when it is desired to refer to the registered character sequence paragraph by paragraph, a space key or a cursor shift key must be depressed to shift the display area so that a 20-character portion of the character sequence to be referred to is displayed on the character display. Thus, it is necessary to shift the display area to the vicinity of the end of the paragraph desired by the operator. This wastes much unnecessary time.